1. Field of the Invention
The present invention relates generally to a communication system, and in particular, to an apparatus and method for detecting a user in a communication system.
2. Description of the Related Art
Generally, the next generation communication system is being developed provide a service capable of transmitting/receiving high-speed, high-capacity data to/from mobile stations (MSs). An Institute of Electrical and Electronics Engineers (IEEE) 802.16e communication system is one of the typical next generation communication systems.
A configuration of the IEEE 802.16e communication system will be described hereinbelow with reference to FIG. 1.
FIG. 1 is a block diagram illustrating a configuration of a typical IEEE 802.16e communication system.
Referring to FIG. 1, the IEEE 802.16e communication system has a multi-cell configuration, i.e., includes a cell 100 and a cell 150, and further includes a base station (BS) 110 for managing the cell 100, a BS 140 for managing the cell 150, and a plurality of MSs 111, 113, 130, 151, and 153. Signal exchanges between the BSs 110 and 140 and the MSs 111, 113, 130, 151, and 153 are achieved using an Orthogonal Frequency Division Multiplexing (OFDM)/Orthogonal Frequency Division Multiple Access (OFDMA). In the following description, it is assumed that the IEEE 802.16e communication system uses OFDMA.
In the IEEE 802.16e communication system, the ranging, especially initial ranging and periodic ranging serve as an important factors to consider. Initial ranging and periodic ranging serve are important factors because they affect user detection and definition of a user parameter, especially a propagation delay parameter, such as a Signal-to-Interference and Noise Ratio (SINR). If the user parameter estimation suffers from an error, sync acquisition fails. As a result, the signal transmitted/received by a corresponding BS serves as interference to sub-channel signals of neighbor BSs, reducing not only the ranging performance but also the overall performance of the IEEE 802.16e communication system.
The IEEE 802.16e communication system, as it uses OFDM/OFDMA, requires ranging sub-channels and ranging codes in order to perform the ranging, and a BS allocates available ranging codes for each type of the ranging. The ranging types are classified into initial ranging, periodic ranging, and bandwidth request ranging. Information on the allocated ranging codes is broadcast to MSs by the BS, and the MSs perform ranging by using the ranging codes according to their purposes based on the information on the ranging codes broadcast by the BS.
Although the ranging codes are classified according to their purposes as described above, the MS uses only a randomly selected one of the classified ranging codes. As a result, in some cases, the same ranging codes transmitted by different MSs may collide with each other. The collision causes not only a decrease in the SINR, but also other problems.
Therefore, in order to correctly estimate the user parameter, it is necessary not only to correctly detect the users performing the ranging, especially the initial ranging and periodic ranging, but also to correctly detect propagation delays of the detected users performing the initial ranging and periodic ranging. Accordingly, there is a need for a system and method for correctly detecting the users performing the initial ranging and periodic ranging, and correctly detecting propagation delays of the detected users performing the initial ranging and periodic ranging.